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  • 1990-1994  (7)
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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analytical method based on a new theoretical model for the x-ray energy responses of silicon surface-barrier (SSB) detectors has been proposed. This method may address a recent confusing issue in the x-ray detection characteristics of SSB semiconductor detectors; that is, the x-ray responses of SSB detectors as well as p-i-n diodes used in underbiased operations were recently found to be contrary to the commonly held belief that the x-ray sensitivity of an SSB detector is determined by the thickness of the depletion layer. The model presented includes a signal contribution from thermally diffusing charge that is created in the field-free substrate region within a diffusion length from the depletion layer along with a signal contribution from charge created in the depletion layer. This model predicts a large signal contribution from the charge-diffusion effect on the SSB responses to high-energy x rays. Formulas and calculated results supporting SSB calibration data have been represented. These analytical methods might be developed to apply the analyses and predictions of energy responses of various types of silicon detectors including p-i-n diodes as well as charge-coupled devices.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of thermal-diffusion charge on the x-ray energy response of silicon surface-barrier (SSB) detectors have generally been ignored; consequently, the SSB response has been believed to be analyzed using the thickness of the depletion layer alone. Our new theory on the SSB x-ray response [J. Appl. Phys. 72, 3363 (1992)] was prepared for addressing recent confusion on plasma x-ray analyses using SSB detectors [Rev. Sci. Instrum. 59, 1380 (1988); 61, 693 (1990); 63, 4850 (1992)]. This approach was made under the assumption of a dominant contribution of the diffusion-charge signal in the vicinity of the x-ray incident location because of the strong reduction of the x-ray produced charge within the thermal-diffusion length. In this report, the comparison between this approximation (having an approximated solution) and the exact numerical calculation (using an integral form) is carried out. Necessity and importance of such three-dimensional treatments for the data analyses as well as the design of multichannel semiconductor-array detectors developed for plasma x-ray tomography diagnostics are highlighted. Furthermore, for the total diffusing-charge amount, the calculated results from our theory and the values using the comment from Donolato agree well within the accuracy of 1%.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 834-841 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical studies are made on dynamics of electrons under electron cyclotron resonance heating (ECRH) by a strong monochromatic wave in a nonuniform magnetic field. The response of the electrons is described in terms of gains in energy and magnetic moment. These expressions are employed to define a response function which connects the velocity distributions of electrons before and after heating in a wide range of conditions. The response function is applied to calculate the velocity distribution of cold electrons which stream up the magnetic slope and are heated at the resonance. This configuration simulates a possible scheme for controlling an inward flux of cold electrons in diverter regions of tori and in mirror ends by mirror reflection enhanced by ECRH. The velocity distribution shows wing-like structures which are not expected from diffusion equations.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3986-3995 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermal dike is a new concept for controlling energy transport carried by electrons along open magnetic field lines by enhancing mirror-reflection with assistance of electron cyclotron resonance heating (ECRH). Quantitative analyses are made to evaluate merits of thermal dike and to clarify requirements for efficient use of it. Heating response function is applied for trajectory analyses of electrons streaming through the ECRH zone. Substantial power gain is obtained under a configuration with a high mirror ratio between the reflection point and the resonance point and with a large scale length of the magnetic gradient in the resonance zone. Thermal dike is shown to be beneficial both in tandem mirrors and in diverters in tori. Discussions are made also on a basic experiment program of thermal dike in the GAMMA 10 tandem mirror.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1677-1680 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Alfvén ion-cyclotron wave excited in the central-cell plasma of the GAMMA 10 tandem mirror is investigated by a reflectometer system. The Fourier amplitude of the instability strongly depends on the anisotropy of the ion velocity distribution function and the plasma β value. The ratio 0.2–0.3 between O-mode and X-mode reflectometer signals suggests that a magnetic fluctuation level similar to the density fluctuation level is excited in the plasma due to the instability.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 866-871 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An empirical scaling for the potential difference between the plug potential ΦP and the floating potential ΦEP of an endplate is obtained in terms of end-loss electron temperatures. Results from the GAMMA 10 tandem mirror [Phys. Rev. Lett. 55, 939 (1985)] indicate that ΔΦ=ΦP−ΦEP scales much better with an effective temperature Teff≡(1−β)TeL+βTeH than with a single temperature TeL or TeH, where TeL and TeH are temperatures of the bulk and the high-energy tail components of the end-loss electrons and β denotes the flux fraction of the TeH component. Moreover, the observed scaling is consistent with a recently developed theoretical model [K. Kurihara et al., J. Phys. Soc. Jpn. 61, 3153 (1992)].
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 936-942 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new type of end-loss-ion energy analyzer (ELA; a multigridded Faraday cup) is applied to measure plasma ion temperatures Tip and plasma potentials ΦP in the GAMMA 10 tandem-mirror device. As compared with conventional-type ELA, this new ELA has obliquely placed ion- and secondary-electron-repeller grids and a collector plate with respect to external tandem-mirror magnetic fields. One of the most useful capabilities of this new ELA for precise ion measurements is to greatly reduce the current of high-energy electrons onto the collector plate. Also, this compact-sized ELA is scannable in the plasma to obtain radial profiles of Tip and ΦP without providing any perturbations of the tandem-mirror magnetic fields because it neither adds its own magnetic field nor needs to shield against the ambient magnetic field. Ion trajectories in the new ELA are numerically calculated so as to make a further understanding of its physics principles and to optimize its design. The energy-calibration experiments for the new ELA are carried out using ion beams; a fairly good agreement in the analyzed beam energies from the new ELA data and from conventional-type ELA data is attained. Furthermore, the first application of the new ELA to plasma diagnostics is made; a substantial reduction in energetic-electron influxes onto real ion signals makes a significant improvement in the analyses of Tip and ΦP.
    Type of Medium: Electronic Resource
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